Table 1 Meta-analysis of the studies that compare the odds of placental P. falciparum infection among individuals with blood group A, B, AB or non-O vs those with blood type O

Primiparae or Multiparae

Active or passive vs none

Adam et al. 2007

293

0.8 (0.44, 1.44)

0.55 (0.27, 1.1)

0.57 (0.21, 1.55)

0.67 (0.41, 1.1)

Loscertales & Brabin, 2006

198

1.35 (0.63, 2.91)

1.17 (0.59, 2.29)

1.58 (0.28, 9.01)

1.26 (0.71, 2.22)

Senga et al. 2007

647

1.32 (0.89, 1.96)

1.22 (0.83, 1.79)

3.68 (1.39, 9.74)

1.35 (0.99, 1.85)

Bedu-Addo et al. 2014

827

1.16 (0.81, 1.66)

1.62 (1.09, 2.39)

1.77 (0.8, 3.91)

1.38 (1.04, 1.85)

Adegnika et al. 2011

378

1.11 (0.39, 3.19)

2.38 (0.91, 6.23)

2.00 (0.23, 17.13)

1.64 (0.75, 3.59)

Ukaga et al. 2007

586

0.72 (0.46, 1.13)

0.68 (0.39, 1.18)

0.21 (0.07, 0.62)

0.61 (0.42, 0.89)

Adam et al. 2009

236

–

–

–

1.25 (0.91, 2.5)

Alim et al. 2015

126

–

–

–

1.11 (0.4, 3.33)

summary OR (95% CI)

0.97 (0.75, 1.19) I² = 8.2%, p = 0.007

1.02 (0.64, 1.40) I² = 58.0%, p = 0.036

0.59 (0.02, 1.14)

I² = 32.9%, p = 0.189

1.01 (0.73, 1.29) I² = 58.8%, p = 0.017

Primiparae

Active vs uninfected

Adam et al. 2007

293

2/31 vs 0/51

0/24 vs 0/51

1/8 vs 0/51

3/50 vs 0/51

Loscertales & Brabin, 2006

198

0.55 (0.15, 1.99)

0.33 (0.10, 1.08)

–

0.41 (0.16, 1.08)

Senga et al. 2007

647

0.31 (0.10, 0.97)

0.79 (0.30, 2.06)

0.93 (0.06, 15.62)

0.54 (0.24, 1.21)

Bedu-Addo et al. 2014

827

2.59 (1.03, 6.50)

1.56 (0.84, 2.91)

4.53 (0.52, 39.74)

1.90 (1.10, 3.28)

Adegnika et al. 2011

378

4.8 (0.73, 31.48)

1.85 (0.16, 2.2)

-

3.2 (0.55, 18.56)

summary OR (95% CI)

0.41 (0.003, 0.82) I² = 1.4%, p = 0.385

1.04 (0.3, 1.78)

I² = 68.9%, p = 0.022

1.42 (−5.81, 8.65)

I² = 0.0%, p = 0.738

0.75 (0.17, 1.34) I² = 53.8%, p = 0.090

Passive vs uninfected

Adam et al. 2007

293

0.46 (0.15, 1.41)

0.31 (0.08, 1.20)

0.87 (0.15, 5.00)

0.44 (0.18, 1.08)

Loscertales & Brabin, 2006

198

2.13 (0.42, 10.73)

1.28 (0.28, 5.93)

–

2.00 (0.55, 7.18)

Senga et al. 2007

647

1.28 (0.58, 2.81)

1.24 (0.54, 2.83)

2.48 (0.26, 23.38)

1.32 (0.67, 2.52)

Bedu-Addo et al. 2014

827

–

–

–

2.23 (1.17, 4.26)

summary OR (95% CI)

0.68 (0.13, 1.22) I² = 0.0%, p = 0.390

0.59 (0.03 1.21) I² = 14.4%, p = 0.331

0.94 (0.44, 3.31) I² = 0.0%, p = 0.789

0.82 (0.08, 1.57) I² = 42.5%, p = 0.176

Active vs passive

Loscertales & Brabin, 2006

198

0.26 (0.05, 1.26)

0.63 (0.27, 1.49)

0.38 (0.04, 3.53)

0.42 (0.2, 0.86)

Senga et al. 2007

647

0.24 (0.08, 0.70)

0.69 (0.31, 1.53)

0.49 (0.05, 4.34)

0.46 (0.23, 0.92)

Bedu-Addo et al. 2014

827

–

–

–

1.44 (0.56, 3.69)

summary OR (95% CI)

0.24 (0.03, 0.52),

I² = 0.0%, p = 0.954

0.66 (0.23, 1.09), I² = 0.0%, p = 0.892

0.42 (0.01, 1.78),

I² = 0.0%, p = 0.938

0.46 (0.23, 0.69)

I² = 0.0%, p = 0.458

Multiparae

Active vs uninfected

Adam et al. 2007

293

3.59 (0.66, 19. 69)

2 (0.26, 15.12)

–

2.37 (0.47, 11.91)

Loscertales & Brabin, 2006

198

1.55 (0.45, 5.34)

2.07 (0.72, 5.93)

2.07 (0.26, 16.27))

1.87 (0.77, 4.56)

Senga et al. 2007

647

1.78 (0.95, 3.35)

1.54 (0.84, 2.86)

5.27 (1.44, 19.32)

1.78 (1.07, 2.96)

Bedu-Addo et al. 2014

827

0.21 (0.11, 0.40)

0.36 (0.19, 0.66)

0.36 (0.12, 1.07)

0.29 (0.17, 0.48)

Adegnika et al. 2011

378

0.51 (0.11, 2.37)

2.59 (0.91, 7.37)

2.44 (0.27, 21.98)

1.36 (0.55, 3.34)

summary OR (95% CI)

0.76 (0.02, 1.54) I² = 51.7%, p = 0.082

1.11 (0.15, 2.07) I² = 52.2%, p = 0.079

0.38 (0.09, 0.86) I² = 0.0%, p = 0.515

1.20 (0.22, 2.19) I² = 72.1%, p = 0.006

Passive vs uninfected

Adam et al. 2007

293

0.56 (0.19, 1.66)

0.99 (0.37, 2.62)

0.47 (0.10, 1.94)

0.70 (0.32, 1.53)

Loscertales & Brabin, 2006

198

3.22 (0.94, 11.05)

2.93 (0.94, 9.13)

–

2.76 (1.04, 7.34)

Senga et al. 2007

647

1.22 (0.58, 2.58)

1.18 (0.58, 2.39)

6.32 (1.71, 23.41)

1.38 (0.78, 2.45)

summary OR (95% CI)

0.82 (0.24, 1.41) I² = 0.0%, p = 0.375

1.16 (0.46, 1.85) I² = 0.0%, p = 0.668

1.01 (0.001, 2.77)

I² = 16.1%, p = 0.304

1.06 (0.38, 1.74) I² = 31.8%, p = 0.231

Active vs passive

Loscertales & Brabin, 2006

198

1.46 (0.6, 3.54)

0.71 (0.21, 2.34)

–

0.68 (0.24, 1.95)

Senga et al. 2007

647

1.46 (0.6, 3.54)

1.31 (0.56, 3.08)

–

1.29 (0.64, 2.59)

Adam et al. 2007

293

5.18 (0.76, 21.87)

2.9 (0.36, 26.39)

–

1.21 (0.16, 9.23)

summary OR (95% CI)

1.49 (0.46, 2.53) I² = 0.0%, p = 0.790

0.97 (0.16, 1.78) I² = 0.0%, p = 0.743

–

0.95 (0.31, 1.59) I² = 0.0%, p = 0.650